The present invention relates to gas-permeable polymeric materials and medical devices comprising the same. In particular, the present invention relates to rigid, gas-permeable ophthalmic devices comprising poly(disubstituted acetylene).
Advances in the chemistry of materials for medical devices have increased their compatibility with a body environment and their comfort for extended use therein. The extended use of ophthalmic devices, such as contact lenses, requires that materials for these lenses allow sufficient rates of transport of oxygen to the cornea to preserve its health because the cornea does not have blood vessels for the supply of oxygen and must receive this gas by its diffusion through the epithelial layer on the outer surface of the cornea.
Most contact lenses fall under two basic categories: rigid lenses and soft lenses. Many lens wearers feel that soft lenses provide better comfort. These lenses are typically made of hydrogel materials, which are polymeric materials capable of retaining a high equilibrium water content. Generally, the higher the water content, the more oxygen reaches the cornea. However, soft lenses having very high water content are difficult to handle. Thus, there may be a practical limit to the oxygen permeability through these lenses. Most soft contact lenses have oxygen permeability (denoted by “Dk” in the contact lens art) in the range of about 60-70 barrers (or 10−10 (cm3 O2 (at STP)·cm)/(cm2·sec·cm Hg)).
On the other hand, certain severe vision defects, such as astigmatism or keratoconus, are better corrected with rigid contact lenses because the materials of these lenses allow for more precise manufacturing and the lenses retain their shapes for a substantially long period. In addition, since the equilibrium water content of rigid, gas-permeable (“RGP”) materials is low, RGP lenses tend not to pull water away from the eye, thus lessen the risk of causing dry eye. The newer RGP lenses can have both some flexibility and gas permeability that is higher than that of soft contact lenses. In order to provide flexibility, polymeric materials of these newer RGP lenses typically include polysiloxane segments that comprise bulky siloxy units such as TRIS (3-methacryloyloxypropyltris(trimethylsiloxy)silane or tris(trimethylsiloxy)silylpropyl methacrylate) or fluorinated siloxy units. Oxygen permeability of about 140 barrers or more can be achieved with these materials. However, polysiloxanes are typically highly hydrophobic and lipophilic. The properties (e.g., lipophilicity, glass transition temperature, mechanical properties) of known polysiloxanes have resulted in contact lenses that adhere to the eye, inhibiting the necessary lens movement. In addition, polysiloxane lipophilicity promotes adhesion to the lens of lipids and proteins in the tear fluid, causing a haze, which interferes with vision through the lens. Finally, as with any family of materials, a limit in oxygen permeability may be reached eventually with these siloxane-based materials.
Therefore, there is a continued need to provide other materials for RGP lenses with improved oxygen permeability. In addition, it is very desirable to provide RGP lenses having improved oxygen permeability and surface wettability.